1. Field of the Invention
The present invention relates to the field of hemo-dialysis apparatus in general and in particular to an arterial-venous graft having an intra-graft stenosis formed therein.
2. Description of Related Art
As can be seen by reference to the following U.S. Pat. Nos. 3,826,257; 4,549,879; 4,753,640; 5,713,859; 6,146,414; 6,461,321 and 6,585,762, the prior art is replete with myriad and diverse graft constructions employed for hemo-dialysis procedures.
While all of the aforementioned prior art constructions are more or less adequate for the basic purpose and function for which they have been specifically designed, they are uniformly deficient with respect to their failure to provide a simple, efficient, and practical means of forming an artificial intra-graft stenosis to provide increased blood flow resistance, and the associated pressure drop, during those periods when the higher blood flow rates required by hemo-dialysis are not present.
As virtually all physicians and health care specialists are aware, the process of hemo-dialysis requires large volumes of blood to be circulated through a filtration device. However, with prior art A-V graft designs having a uniform bore, the continued high velocity and high pressure blood flow into veins creates venous irritation and scarring leading to stenosis and eventual occlusion as well as causing increased cardiac demands.
Additionally, current dialysis shunts provide a continuous high flow which bypasses the patient's normal tissues and directs high pressure blood flow into the normally low pressure veins. This shunt creates what is called in medicine a “steal.” The blood flowing through the shunt bypasses tissues and then returns to the heart. This creates undue, continued stress on the heart and can invoke a situation in which the blood flow to the hand and/or arm is compromised.
Stanish, in U.S. Pat. No. 6,585,762 discloses a graft comprising, in the streamwise direction, a diverging portion followed by a lumen of substantially constant diameter, followed by a converging portion. Because the constant diameter lumen portion of the graft has a diameter greater than the ends, the pressure drop across the Stanish graft is minimized.
Buselmeier, in U.S. Pat. No. 3,826,257 discloses a converging portion followed by a lumen having a substantially constant diameter, followed by a diverging portion. The hemo-dialysis machine access tubes are located between the converging and diverging portions, in the constant diameter lumen. This arrangement, however, defeats the purpose of the flow restrictions as almost no pressure drop exists between the two ports of the access tubes. Blood will flow through the constant diameter lumen instead of, or in opposing direction to, the dialysis machine. The flow restriction must reside between the dialysis machine's access tubes to effect the needed pressure drop.
As a consequence of the foregoing situation, there has existed a longstanding need among medical personnel for a new and improved A-V stent graft construction having a reduced diameter portion, either of fixed diameter or variable diameter, and the provision of such a construction is the stated objective of the present invention.